Method for reducing a release of environmental contaminants through a thief hatch

ABSTRACT

A method for reducing a release of environmental contaminants through a thief hatch is described. The method involves a step of securing a drainage conduit to a storage tank to divert environmental contaminants from a top of a storage tank to a contaminant capture area below. A further step involves positioning a riser on the drainage conduit toward the top of the storage tank. A final step involves mounting a thief hatch at a remote end of the riser.

FIELD

There is described a method for reducing a release of environmental contaminants through a thief hatch, along with a modified thief hatch and a storage tank-thief hatch combination.

BACKGROUND

Storage vessels have a pressure sensitive closure on top, which has come to be known as a “thief hatch”. In order to avoid an explosion caused by a pressure build up within a storage vessel, the thief hatch is set to open above a preset pressure threshold. Thief hatches are commonly found with petroleum storage vessels. When the preset pressure threshold is reached and the thief hatch opens, petroleum sprays into the air and then flows down the side of the storage vessel.

U.S. Pat. No. 4,162,020 (Kirkland) describes an anti-spill device that was developed to avoid environmental contamination when the thief hatch opens and petroleum under pressure is released through the thief hatch. The anti-spill device of the Kirkland reference is a pan that can be installed on or around the thief hatch to allow for the containment of the escaping liquid and to provide for the transfer of such liquid to a safe and environmentally suitable location. There will hereinafter be described an alternative to the Kirkland device.

SUMMARY

According to one aspect there is provided a method for reducing a release of environmental contaminants through a thief hatch. The method involves a step of securing a drainage conduit to a storage tank to divert environmental contaminants from a top of a storage tank to a contaminant capture area below. A further step involves positioning a riser on the drainage conduit toward the top of the storage tank. A final step involves mounting a thief hatch at a remote end of the riser.

With the method, as described above, foaming within the storage tank is accommodated by the drainage conduit which diverts any overflow of foam to a contaminant capture area below. Should there be a rapid build up of pressure that triggers a release of the thief hatch, a majority of the liquid released is diverted to the contaminant capture area via the drainage conduit.

Once it was determined that most of the liquid released through the thief hatch could be diverted through the drainage conduit to the contaminant capture area, consideration was given as to how to further reduce the release of contaminants. It was determined that the height of the riser could be selected to reduce the likelihood that liquids flowing along the drainage conduit would reach the remote end of the rise where the thief hatch is positioned. It was also determined that a deflector could be positioned to deflect liquids flowing along the drainage conduit away from an inlet end of the riser, thereby reducing the likelihood that liquids flowing along the drainage conduit will reach the remote end of the rise where the thief hatch is positioned.

According to another aspect of the invention there is provided a thief hatch assembly that was constructed for installation on a storage tank in accordance with the teachings of the method. According to yet another aspect of the invention there is provided a combination of a storage tank on which the thief hatch assembly is installed.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features will become more apparent from the following description in which reference is made to the appended drawings, the drawings are for the purpose of illustration only and are not intended to be in any way limiting, wherein:

FIG. 1 is a side elevation view of a storage tank on which a thief hatch assembly has been installed in accordance with the teachings of the present method.

FIG. 2 is a detailed side elevation, in section, of a first alternative thief hatch assembly with the deflector before the thief hatch.

FIG. 3 is a detailed side elevation, in section, of a second alternative thief hatch assembly with the deflector on the backside of the thief hatch.

FIG. 4 is a detailed side elevation view of a third alternative thief hatch assembly with a heightened riser.

DETAILED DESCRIPTION

A thief hatch assembly, developed in accordance with the teaching of the method and generally identified by reference numeral 10, will now be described with reference to a storage tank 100 illustrated in FIG. 1, three variations will then be described with reference to FIG. 2, FIG. 3, and FIG. 4.

Structure and Relationship of Parts:

Referring to FIG. 1, the thief hatch assembly 10 has a drainage conduit 12 with a first end or inlet end 14 and a second end or outlet end 16. The first end 14 is attached to a storage tank 100 by a coupling 18. The storage tank 100 has a top 102, a base 104, and a peripheral side tank wall 106. Pressure may build up inside storage tank 100 and the thief hatch assembly 10 facilitates the diversion of environmental contaminants from storage tank 100 to a contaminant capture area 110. The first end or inlet end 14 of thief hatch assembly 10 is connected to the top 102 of storage tank 100 and the environmental contaminants may flow through drainage conduit 12 to the second end or outlet end 16 where the contaminant capture area 110 is located. Drainage occurs by the force of gravity acting on the liquid inside the drainage conduit 12. The drainage conduit 12 has a riser 20 with a conduit communication end 22 and a remote end 24. In the illustrated embodiment, the drainage conduit 12 has a shape that resembles a “cane” and riser 20 is located at the apex of the handle of the “cane”. The conduit communication end 22 connects riser 20 to the drainage conduit 12. A thief hatch 26 is located at remote end 24 of riser 20. Thief hatch 26 allows for the venting of gases that build up inside storage tank 100.

Referring to FIG. 2, there is illustrated a first alternative embodiment in which a deflector 32 is located at the conduit communication end 22 of the riser. Deflector 32 is positioned to deflect liquids flowing along drainage conduit 12 away from conduit communication end 22 of riser 20. Deflector 32 extends outward diagonally from conduit communication end 22 of riser 20 towards a middle of the portion of drainage conduit 12 that is directly below riser 20 so that the flow of liquids into riser 20 is discouraged by deflector 32.

Referring to FIG. 3, there is illustrated a second alternative embodiment in which a deflector 34 extends inward diagonally from conduit communication end 22 of riser 20 towards a middle of riser 20 so that that the flow of liquids into the riser is discouraged by deflector 34.

It will be appreciated that deflector 32 depicted in FIG. 2 and deflector 34 depicted in FIG. 3, reduce the likelihood that liquids flowing along drainage conduit 12 will reach remote end 24 of riser 20 where thief hatch 26 is positioned. Those skilled in the art would be aware of other deflector configurations that would be capable of achieving this result.

Referring to FIG. 4, there is illustrated a third alternative embodiment in which riser 20 is taller than in the other embodiments. It is the provision of this tall riser that is used as an alternative to deflectors 32 or 34 to reduce the likelihood that liquids flowing along the drainage conduit 12 will reach remote end 24 of riser 20 where the thief hatch 26 is positioned. It is believed that when a height of the riser is over 6 inches, it is approaching a height that reduces the likelihood that liquids flowing along the drainage conduit 12 will reach the remote end 24 of riser 20 where thief hatch 26 is positioned. It will be appreciated that the height of riser 20 required to achieve the desired result will depend on factors such as the viscosity of the fluid, pressure attained and there are other factors that would be known to those skilled in the art to determine the height of riser required to achieve the desired result.

Operation:

Referring to FIG. 1, thief hatch assembly 10 has been developed in accordance with the teachings of a method for reducing a release of environmental contaminants through a thief hatch. The method involves a step of securing drainage conduit 12 to storage tank 100 to divert environmental contaminants from top 102 of storage tank 100 to contaminant capture area 110 below. Riser 20 is positioned on drainage conduit 12 toward top 102 of storage tank 100. Instead of being attached directly to top 102 of storage tank 100, thief hatch 26 is positioned at remote end 24 of riser 20.

Foaming within storage tank 100 is accommodated by drainage conduit 12 which diverts any overflow of foam to contaminant capture area 110. In the event that there is a rapid build up of pressure that triggers a release of thief hatch 26, a majority of the liquid released is diverted to contaminant capture area 110 via drainage conduit 12, instead of being blown into the atmosphere where it may be carried by the wind.

This teaching will reduce the amount of liquid reaching thief hatch 26. One skilled in the art will appreciate that if one can reduce or eliminate the amount of liquid reaching thief hatch 26, one can reduce or eliminate environmental contamination. As described above, there are various methods that can be used to prevent liquids from reaching thief hatch 26. Retelling to FIG. 2 and FIG. 3, deflectors 32 or 34 may be used to discourage entry of liquids into riser 20. Referring to FIG. 4, with sufficient knowledge of viscosity, flow rates, pressure, and the like, one skilled in the art is capable of selecting a riser that is of a sufficient height that it is unlikely that liquids will reach thief hatch 26 except in the more extraordinary of circumstances.

In this patent document, the word “comprising” is used in its non-limiting sense to mean that items following the word are included, but items not specifically mentioned are not excluded. A reference to an element by the indefinite article “a” does not exclude the possibility that more than one of the element is present, unless the context clearly requires that there be one and only one of the elements.

The scope of the claims should not be limited by the illustrated embodiments set forth as examples, but should be given the broadest interpretation consistent with a purposive construction of the claims in view of the description as a whole. 

What is claimed is:
 1. A method for reducing a release of environmental contaminants through a thief hatch, comprising, securing a drainage conduit to a storage tank to divert environmental contaminants from a top of a storage tank to a contaminant capture area below; positioning a riser on the drainage conduit toward the top of the storage tank; and mounting a thief hatch at a remote end of the riser.
 2. The method of claim 1, wherein the height of the riser is selected to reduce the likelihood that liquids flowing along the drainage conduit will reach the remote end of the rise where the thief hatch is positioned.
 3. The method of claim 1, wherein a deflector is positioned to deflect liquids flowing along the drainage conduit away from an inlet end of the riser, thereby reducing the likelihood that liquids flowing along the drainage conduit will reach the remote end of the riser where the thief hatch is positioned.
 4. A thief hatch assembly, comprising: a drainage conduit having a first end and a second end; a coupling at the first end for connecting the drainage conduit; a riser on the drainage conduit toward the first end; and a thief hatch at a remote end of the riser.
 5. The thief hatch of claim 1, wherein the height of the riser is over 6 inches to reduce the likelihood that liquids flowing along the drainage conduit will reach the remote end of the rise where the thief hatch is positioned.
 6. The thief hatch of claim 1, wherein a deflector is positioned to deflect liquids flowing along the drainage conduit away from the inlet end of the riser, thereby reducing the likelihood that liquids flowing along the drainage conduit will reach the remote end of the rise where the thief hatch is positioned.
 7. A storage tank and thief hatch combination comprising: a liquid retaining storage tank having a base, a top and a peripheral sidewall; a drainage conduit secured to the storage tank to divert environmental contaminants from a top of a storage tank down the sidewall by gravity drainage to a contaminant capture area below, the drainage conduit having a first or inlet end and a second or outlet end; a riser positioned on the drainage conduit toward the inlet end at the top of the storage tank, the riser having a conduit communication end and a remote end; and a thief hatch positioned at the remote end of the riser.
 8. The combination of claim 1, wherein the height of the riser is selected to reduce the likelihood that liquids flowing along the drainage conduit will reach the remote end of the rise where the thief hatch is positioned.
 9. The method of claim 1, wherein a deflector is positioned to deflect liquids flowing along the drainage conduit away from the inlet end of the riser, thereby reducing the likelihood that liquids flowing along the drainage conduit will reach the remote end of the rise where the thief hatch is positioned. 